/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.LinkedHashMap;

/**
 * A {@code Multiset} implementation with predictable iteration order. Its iterator orders elements
 * according to when the first occurrence of the element was added. When the multiset contains
 * multiple instances of an element, those instances are consecutive in the iteration order. If all
 * occurrences of an element are removed, after which that element is added to the multiset, the
 * element will appear at the end of the iteration.
 *
 * <p>
 * See the Guava User Guide article on
 * <a href= "https://github.com/google/guava/wiki/NewCollectionTypesExplained#multiset">
 * {@code Multiset}</a>.
 *
 * @author Kevin Bourrillion
 * @author Jared Levy
 * @since 2.0
 */
@GwtCompatible(serializable = true, emulated = true)
@SuppressWarnings("serial") // we're overriding default serialization
public final class LinkedHashMultiset<E> extends AbstractMapBasedMultiset<E> {

    /**
     * Creates a new, empty {@code LinkedHashMultiset} using the default initial capacity.
     */
    public static <E> LinkedHashMultiset<E> create() {
        return new LinkedHashMultiset<E>();
    }

    /**
     * Creates a new, empty {@code LinkedHashMultiset} with the specified expected number of
     * distinct elements.
     *
     * @param distinctElements the expected number of distinct elements
     * @throws IllegalArgumentException if {@code distinctElements} is negative
     */
    public static <E> LinkedHashMultiset<E> create(int distinctElements) {
        return new LinkedHashMultiset<E>(distinctElements);
    }

    /**
     * Creates a new {@code LinkedHashMultiset} containing the specified elements.
     *
     * <p>
     * This implementation is highly efficient when {@code elements} is itself a {@link Multiset}.
     *
     * @param elements the elements that the multiset should contain
     */
    public static <E> LinkedHashMultiset<E> create(Iterable<? extends E> elements) {
        LinkedHashMultiset<E> multiset = create(Multisets.inferDistinctElements(elements));
        Iterables.addAll(multiset, elements);
        return multiset;
    }

    private LinkedHashMultiset() {
        super(new LinkedHashMap<E, Count>());
    }

    private LinkedHashMultiset(int distinctElements) {
        super(Maps.<E, Count>newLinkedHashMapWithExpectedSize(distinctElements));
    }

    /**
     * @serialData the number of distinct elements, the first element, its count, the second
     *             element, its count, and so on
     */
    @GwtIncompatible // java.io.ObjectOutputStream
    private void writeObject(ObjectOutputStream stream) throws IOException {
        stream.defaultWriteObject();
        Serialization.writeMultiset(this, stream);
    }

    @GwtIncompatible // java.io.ObjectInputStream
    private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
        stream.defaultReadObject();
        int distinctElements = Serialization.readCount(stream);
        setBackingMap(new LinkedHashMap<E, Count>());
        Serialization.populateMultiset(this, stream, distinctElements);
    }

    @GwtIncompatible // not needed in emulated source
    private static final long serialVersionUID = 0;
}
